Plug-in/Code to Generate Meta Description from Excerpt?

I’ve been looking at how my sites show up in search engines and the description is not usually very enticing or relevant – I have an idea on how to fix it but no idea how to actually do it or if it is possible.

This article from Google explains using the meta description and how your listings show up & their suggestions:
https://googlewebmastercentral.blogspot.com/2007/09/improve-snippets-with-meta-description.html

Ideally I’d like a plug-in that on the home page has a general site description, and then on the individual posts page generate the meta description directly from what you write in the excerpt box when writing posts…that way you’d see a nice summary that’s relevant & would make people want to visit your site. It would probably also help with SEO for a lot of people as well.

Anybody have any suggestions on how to do this or if it is possible? (With or without a plug-in?)

Thanks in advance!